An electrophotographic technique is used not only in the field of copying machines but also widely in the field of various printers in recent years from the viewpoint of immediacy, high quality of images, etc. Formation of a visible image by an electrophotographic system is carried out usually by firstly forming an electrostatic latent image on a photoreceptor such as a drum or a belt, then developing it with a toner, then transferring it to a transfer medium such as a transfer paper, and then fixing the toner to the transfer medium by e.g. heating by a fixing roller.
Various performances are required for copying machines, printers or the like, but a problem of an odor emitted from such development devices has become serious more than ever in the present office environment in which a plurality of development devices are always in operation. As one of factors for the odor emitted from a development device, an odor attributable to a toner may be mentioned, and it is considered that the odor is emitted particularly during the above-mentioned heating for fixing.
To reduce the odor of the toner, various studies have been made. For example, there have been a method wherein low volatile components are degassed during the kneading at the time of producing a toner by a melt-kneading pulverization method, and a method wherein attention is paid to the residual monomer, the remaining solvent or benzaldehyde, and the weight fraction thereof in the toner is reduced (Patent Document 1). Further, in a suspension polymerization method or an emulsion polymerization flocculation method, wherein toner particles are granulated in water, it is known to adopt a method wherein the residual monomer is reduced by increasing the monomer addition rate during the polymerization, or deaeration is carried out during the drying. For example, in the case of producing a toner by a suspension polymerization method, (1) a method of accelerating the consumption of the polymerizable monomer at the time when the conversion for polymerization has reached at least 95%, and (2) a method of removing the organic solvent, the polymerizable monomer or their mixture from the toner particles, are known (Patent Document 2).
Patent Document 1: JP-A-3-101746
Patent Document 2: JP-A-5-197193
On the other hand, along with the trend for high speed of copying machines in recent years, it has been attempted to raise the temperature at the fixing portion to carry out the fixing at a high speed. Usually, if fixing is carried out at a high temperature, a phenomenon (high temperature offset) is likely to result wherein the toner will attach to the fixing component. To prevent such high temperature offset, it is common to employ a technique wherein the molecular weight of a resin constituting the main component of the toner is increased (Patent Document 3). As a method to increase a high molecular weight component, a method for polymerization at a low temperature is, for example, known.
Patent Document 3: JP-A-63-115435